Inks comprising a water-dispersed resin, a water-dispersible colorant and water are known in the art. Such ink compositions are also known as latex inks. Latex inks may be used for printing images onto a receiving medium, for example using ink jet printing. Latex inks are known to give robust images, due to a layer of polymer particles that is formed on the surface of the receiving medium protecting the colorant particles.
A known problem of latex inks is that the properties of the ink within the print head may deteriorate upon evaporation of water. Because evaporation of water, the ink composition may thicken, leading e.g. to a viscosity increase or precipitation of solid particles from the ink composition may occur, decreasing the jetting stability.
It is known to add co-solvents to a latex ink, which results in a latex ink having a liquid vehicle comprising water and one or more co-solvents. The addition of such co-solvent may result in slowing down the evaporation of the liquid vehicle. The co-solvent may also assist in stabilization of the pigment particles and/or the water dispersed resin particles in the ink composition, preventing the formation of solid precipitates.
When the ink has been applied onto the recording medium, e.g. by jetting droplets of the ink composition onto the recording medium, then the ink has to dry. As a consequence, the liquid vehicle, comprising water and the at least one co-solvent, need to be removed. This may be done by absorption in the recording medium and/or evaporation of the liquid vehicle. However, absorption of the liquid vehicle by the recording medium may only be possible when the recording medium is a porous medium. If the recording medium is a non-porous medium, no liquid may be absorbed by the medium. In the latter case, all solvents present may need to be removed by evaporation.
This is a disadvantage from several points of view. For example, evaporation of liquids consumes energy. In addition, by evaporating a co-solvent, vapors of this co-solvent are formed. Vapors of co-solvents may be harmful from a health, safety & environmental (HSE) point of view. For example, these vapors may be toxic and/or flammable.
It is therefore an object to provide an ink composition that requires less energy when drying. It is a further object of the invention to provide an ink composition that forms no or only little harmful vapors. It is a further object of the invention to provide an ink composition which is stable in the print head. It is a further object of the invention to provide an ink composition which allows fast drying of the ink after printing. It is a further object of the invention to provide an ink composition which provides robust images.